Matching Items (5)
Filtering by
- All Subjects: Economics
- All Subjects: Chytridiomycosis
Description
Epidemiological theory normally does not predict host extinction from infectious disease because of a host density threshold below which pathogens cannot persist. However, host extinction can occur when a biotic or abiotic pathogen reservoir allows for density-independent transmission. Amphibians are facing global population decline and extinction from the emerging infectious disease chytridiomycosis, caused by the fungus Batrachochytrium dentrobatidis (Bd). I use the model species Eleutherodactylus coqui to assess the impact of Bd on terrestrial direct-developing frog species, a common life history in the tropics. I tested the importance of two key factors that might influence this impact and then used laboratory experiments and published field data to model population-level impacts of Bd on E. coqui. First, I assessed the ontogenetic susceptibility of E. coqui by exposing juvenile and adult frogs to the same pathogen strain and dose. Juveniles exposed to Bd had significantly lower survival rates compared with control juveniles, while adult frogs often cleared infection. Second, I conducted experiments to determine whether E. coqui can become infected with Bd indirectly from contact with zoospores shed onto vegetation by an infected frog and from direct exposure to an infected frog. Both types of transmission were observed, making this the first demonstration that amphibians can become infected indirectly in non-aquatic habitats. Third, I tested the hypothesis that artificially-maintained cultures of Bd attenuate in pathogenicity, an effect known for other fungal pathogens. Comparing two cultures of the same Bd strain with different passage histories revealed reduced zoospore production and disease-induced mortality rates for a susceptible frog species (Atelopus zeteki) but not for the less-susceptible E. coqui. Finally, I used a mathematical model to project the population-level impacts of chytridiomycosis on E. coqui. Model analysis showed that indirect transmission, combined with either a high rate of zoospore production or low rate of zoospore mortality, is required for Bd to drive E. coqui populations below an extinction threshold. High rates of transmission plus frequent re-infection could lead to poor recruitment of infected juveniles and population decline. My research adds further insight into how emerging infectious disease is contributing to the loss of amphibian biodiversity.
ContributorsLanghammer, Penny F. (Author) / Collins, James P. (Thesis advisor) / Brooks, Thomas M (Committee member) / Burrowes, Patricia A. (Committee member) / Anderies, John M (Committee member) / Escalante, Ananias A (Committee member) / Smith, Andrew T. (Committee member) / Arizona State University (Publisher)
Created2013
Description
Sustainability depends in part on our capacity to resolve dilemmas of the commons in Coupled Infrastructure Systems (CIS). Thus, we need to know more about how to incentivize individuals to take collective action to manage shared resources. Moreover, given that we will experience new and more extreme weather events due to climate change, we need to learn how to increase the robustness of CIS to those shocks. This dissertation studies irrigation systems to contribute to the development of an empirically based theory of commons governance for robust systems. I first studied the eight institutional design principles (DPs) for long enduring systems of shared resources that the Nobel Prize winner Elinor Ostrom proposed in 1990. I performed a critical literature review of 64 studies that looked at the institutional configuration of CIS, and based on my findings I propose some modifications of their definitions and application in research and policy making. I then studied how the revisited design principles, when analyzed conjointly with biophysical and ethnographic characteristics of CISs, perform to avoid over-appropriation, poverty and critical conflicts among users of an irrigation system. After carrying out a meta-analysis of 28 cases around the world, I found that particular combinations of those variables related to population size, countries corruption, the condition of water storage, monitoring of users behavior, and involving users in the decision making process for the commons governance, were sufficient to obtain the desired outcomes. The two last studies were based on the Peruvian Piura Basin, a CIS that has been exposed to environmental shocks for decades. I used secondary and primary data to carry out a longitudinal study using as guidance the robustness framework, and different hypothesis from prominent collapse theories to draw potential explanations. I then developed a dynamic model that shows how at the current situation it is more effective to invest in rules enforcement than in the improvement of the physical infrastructure (e.g. reservoir). Finally, I explored different strategies to increase the robustness of the system, through enabling collective action in the Basin.
ContributorsRubinos, Cathy (Author) / Anderies, John M (Thesis advisor) / Abbott, Joshua K (Committee member) / Janssen, Marcus A (Committee member) / Arizona State University (Publisher)
Created2017
Description
Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing chytridiomycosis, is the cause of massive amphibian die-offs. As with any host-pathogen relationship, it is paramount to understand the growth and reproduction of the pathogen that causes an infectious disease outbreak. The life-cycle of the pathogen, Bd, is strongly influenced by temperature; however, previous research has focused on Bd isolated from limited geographic ranges, and may not be representative of Bd on a global scale. My research examines the relationship between Bd and temperature on the global level to determine the actual thermal maximum of Bd. Six isolates of Bd, from three continents, were incubated at a temperature within the thermal range (21°C) and a temperature higher than the optimal thermal range (27°C). Temperature affected the growth and zoosporangium size of all six isolates of Bd. All six isolates had proliferative growth at 21°C, but at 27°C the amount and quality of growth varied per isolate. My results demonstrate that each Bd isolate has a different response to temperature, and the thermal maximum for growth varies with each isolate. Further understanding of the difference in isolate response to temperature can lead to a better understanding of Bd pathogen dynamics, as well as allow us the ability to identify susceptible hosts and environments before an outbreak.
ContributorsWoodland, Laura Elizabeth (Author) / Collins, James (Thesis director) / Davidson, Elizabeth (Committee member) / Roberson, Robert (Committee member) / School of Politics and Global Studies (Contributor) / School of Molecular Sciences (Contributor) / Barrett, The Honors College (Contributor)
Created2016-12
Description
Nature-based recreation is a popular way for people to interact with the environment that also confers numerous economic and health benefits. It is important that the social-ecological systems (SES) that host nature-based recreation be managed effectively, both to preserve the benefits of this important human-environment interaction, and to avoid the potential negative outcomes of recreational commons. The SES that host nature-based recreation are characterized by complex and dynamic feedbacks that complicate their management. Managing these systems is made more complex by the suite of external, multi-scalar, and anthropogenic forces (e.g., climate change, trans-boundary pollution) that plague them with increasing frequency. This dissertation investigates the importance of accounting for this full range of system feedbacks when managing for nature-based recreation. I begin with a broad discussion of the types of dilemmas faced by managers of nature-based recreation. I create a systems-thinking typology of management dilemmas that apply across different recreation modes and system contexts, and which are characterized as feedbacks within the broader recreational system. My findings in this chapter have important implications for understanding and anticipating how different exogenous and endogenous shocks (including management interventions, themselves) may work through or change the processes in SES that host nature-based recreation. In the following two chapters, I narrow my focus to examine case studies of specific dilemma archetypes and proposed management interventions. First, I perform an ex ante analysis of a prospective policy response to a regulatory spiral of excess recreational fishing effort and abridged fishing seasons in the U.S. Gulf of Mexico. I estimate behavioral models of fishers’ responses to a prospective incentive-based intervention, and find evidence that such a policy could improve multiple fishery outcomes. Second, I perform an ex post program evaluation of an invasive species bounty program. My results suggest that the program underperformed because it failed to overcome countervailing incentives. Together, my case study analyses reveal the value of modeling for designing policy for these complex SES and show the importance of accounting for the full set of system feedbacks (including the incentives that drive recreator behaviors and the impacts of those behaviors) when managing nature-based recreation.
ContributorsJungers, Brenna (Author) / Abbott, Joshua K (Thesis advisor) / Leonard, Bryan (Committee member) / Anderies, John M (Committee member) / Bair, Lucas S (Committee member) / Arizona State University (Publisher)
Created2023
Description
In many social-ecological systems, shared resources play a critical role in supporting the livelihoods of rural populations. Physical infrastructure enables resource access and reduces the variability of resource supply. In order for the infrastructure to remain functional, institutions must incentivize individuals to engage in provision and maintenance. The objective of my dissertation is to understand key formal and informal institutions that affect provision of shared infrastructure and the policy tools that may improve infrastructure provision. I examine these questions in the context of irrigation systems in India because infrastructure maintenance is a persistent challenge and system function is critical for global food production.
My first study investigates how the presence of private infrastructure, such as groundwater pumps, affects the provision of shared infrastructure, such as shared tanks or surface reservoirs. I examine whether formal institutions, such as water pricing instruments, may prevent under-provision of the shared tanks. My findings suggest that in the absence of rules that coordinate tank maintenance, the presence of private pumps will have a detrimental effect on system productivity and equality. On the other hand, the combination of a fixed groundwater fee and a location-based maintenance fee for tank users can improve system productivity and equality.
The second study examines the effect of power asymmetries between farmers, caused by informal institutions such as caste, on the persistence of political institutions that govern infrastructure provision. I examined the effect of policy tools, such as non-farm wage employment and informational interventions, on the persistence of two types of political institutions: self-governed and nested. Results suggest that critical regime shifts in political institutions can be generated by either intervening in formal institutions, such as non-farm wage employment, or informal institutions, such as knowledge transmission or learning mechanisms.
The third study investigates how bureaucratic and political corruption affect public good provision. I examine how institutional and environmental factors affect the likelihood of corruption and infrastructure provision. I demonstrate that cracking down on corruption is only beneficial when infrastructure provision is poor. I also show that bureaucratic wages play an important role in curbing extralegal transactions and improving infrastructure provision.
My first study investigates how the presence of private infrastructure, such as groundwater pumps, affects the provision of shared infrastructure, such as shared tanks or surface reservoirs. I examine whether formal institutions, such as water pricing instruments, may prevent under-provision of the shared tanks. My findings suggest that in the absence of rules that coordinate tank maintenance, the presence of private pumps will have a detrimental effect on system productivity and equality. On the other hand, the combination of a fixed groundwater fee and a location-based maintenance fee for tank users can improve system productivity and equality.
The second study examines the effect of power asymmetries between farmers, caused by informal institutions such as caste, on the persistence of political institutions that govern infrastructure provision. I examined the effect of policy tools, such as non-farm wage employment and informational interventions, on the persistence of two types of political institutions: self-governed and nested. Results suggest that critical regime shifts in political institutions can be generated by either intervening in formal institutions, such as non-farm wage employment, or informal institutions, such as knowledge transmission or learning mechanisms.
The third study investigates how bureaucratic and political corruption affect public good provision. I examine how institutional and environmental factors affect the likelihood of corruption and infrastructure provision. I demonstrate that cracking down on corruption is only beneficial when infrastructure provision is poor. I also show that bureaucratic wages play an important role in curbing extralegal transactions and improving infrastructure provision.
ContributorsVallury, Sechindra (Author) / Abbott, Joshua K (Thesis advisor) / Anderies, John M (Thesis advisor) / Leonard, Bryan (Committee member) / Arizona State University (Publisher)
Created2019